1. Field of the Invention
The present invention relates to a water-based pigment dispersion, a method for producing the water-based pigment dispersion, a water-based pigment ink, a method for producing the water-based pigment ink, an ink record, an inkjet recording apparatus, and an inkjet recording method.
2. Description of the Related Art
An inkjet recording method has advantages over other recording methods in that it facilitates full-colorization because of the process that is simpler than those of other recording methods and in that high-resolution images can be obtained even with a simply structured apparatus. As for inkjet inks, dye-based inks of which various water-soluble pigments are dissolved in water or a mixture solution of water and an organic solvent are used, however, dye-based inks suffer from the disadvantage of being poor in resistance to light, although it excels in color tone definition. On the other hand, pigment-based inks in which carbon black and various organic pigments are dispersed are more and more studied because pigment-based inks are superior to dye-based inks in terms of resistance to light.
However, unlike dyes, pigments are water-insoluble, and thus it is important to stably disperse pigments in water in particulate state, however, such dispersion is not exactly easy to achieve. Particularly when temperature conditions of a pigment dispersion system are changed, the absorption equilibrium of pigments relative to the dispersing agent is unbalanced, and this affects interaction of pigment particles with each other and may bring about changes in physical properties in storage over a long period of time and/or occurrence of agglutinated foreign matters. Such physical property changes, particularly changes in viscosity, and/or such occurrences of a large amount of agglutinated foreign matters are deadly to inkjet printer inks. This is because thy cause changes in ink properties at inkjet heads and/or clogging of ejection nozzles, and so it may defy proper printing.
As a way to solve the problem with such changes in physical properties and/or occurrences of agglutinated foreign matters, for example, Japanese Patent Application Laid-Open (JP-A) No. 03-64376 discloses a method for preliminarily preventing agglutinated foreign matters that will arise under long-term storage conditions by heating a pigment-based ink at 50° C. for 100 hours to 500 hours.
Japanese Patent Application Laid-Open (JP-A) No. 08-73785 enables a short-time heating process in which pigments, an insoluble resin emulsion, and saccharides are heated at a temperature of 65° C. to 80° C. for a short length of time of 0.5 hours to 3 hours.
Japanese Patent Application Laid-Open (JP-A) No. 2002-30243 enables providing a pigment ink causing relatively less changes in viscosity after storage over a long period of time by heating a pigment, water, and a polysaccharide in an aqueous solution with a pH of 8 or more at temperatures of 60° C. to 180° C.
In addition, Japanese Patent Application Laid-Open (JP-A) No. 2003-313475 enables providing a pigment ink which has a sharp particle diameter distribution and excels in ink glossiness and color reproductivity by heating a colored particulate dispersion ink containing color materials and a resin at a temperature of 35° C. or more.
However, with a particulate pigment ink having a particle diameter of 150 nm or less, or a pigment ink of surfactant dispersion type, it is impossible to prevent occurrences of agglutinated foreign matters and overall changes in physical properties thereof i.e. deterioration of the pigment ink.